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Effect of low BMI on health status

In Study III carried out in 1990, we followed the change of food intake and weight gain of the mothers during pregnancy, some biochemical indicators of nutritional status and the weight of newborn babies. Results indicated (Hop et al., 1991) that the average weight gain of mothers during pregnancy in rural areas is 6.4 kg and in Hanoi city 8.5 kg. The study also revealed a relation between weight gain during pregnancy and the weight of newborn at different values of the mother's BMI before pregnancy (Table 10).

Study IV assessed the health status of women at reproductive age in two communes in rural areas in the north of Vietnam. In the sample of 400 subjects, aged 18-49 years, the mothers with a high parity were more likely to have CED than the others (Khoi et al., 1993) (Table 11).

Toan et al. (1992) also carried out studies on the nutritional and health status of 605 adults aged >45 years in Thanh Hoa province and the cut-off point of BMI at 18.5 was used to classify the nutritional status with a systematic subsample for biochemical examination. They found that the older the people, the lower their BMI and that when the BMI value was <18.5 the rate of morbidity was higher and digestive diseases more common.

Table 10. Relation between body mass index (BMI) of mothers before pregnancy and weight gained during pregnancy and birth weight

Weight gained during pregnancy

Newborn weight (g) by mothers' prepregnancy BMI levels




<8 kg




(n = 21)

(n = 34)

>8 kg




(n = 19)

(n = 40)

We have found that:

1. BMI has a relationship with age, sex, socioeconomic condition and pattern of food intake and is a good indicator of nutritional status and health development.

2. BMI decreases with age in rural populations but increases in urban ones. Such different patterns can be the result of various factors but are linked to the fact that people in rural populations have little fat reserves and the energy balance is often negative due to heavy physical work.

3. Body mass also decreases with the number of pregnancies.

Since nutritional status of adults directly affects productivity, work performance and well-being of the community, it should receive more attention in both methodology and practice.

Table 11. Relationship between the mothers' body mass index (BMI) and the number of their children

Percentage of women in BMI classes

No. of children in family

³ 18.5

























By using the BMI as an indicator for evaluation of nutritional status of adults, we find out that:

1. The mean value of BMI of adults aged from 26 to 40 years is about 19.7 in both sexes but it decreases thereafter in rural areas.

2. CED is still widespread in Vietnam according to Ferro-Luzzi/James classification. The mean value of CED is ±40% but this percentage varies with age, sex and socioeconomic condition.

3. There is a significant relationship between the grade of CED in mothers and the nutritional status of their <5-year-old children. Some findings revealed the relationship between maternal BMI and birth weight, between CED with health status and morbidity.

4. The proposed cut-off point of Ferro-Luzzi/James in the classification of CED is likely to be acceptable in Vietnam.


FAO/WHO/UNU (1985): Energy and protein requirements. Technical report series no 724. Geneva: WHO.

Ferro-Luzzi A, Sette s, Franklin M & James WPT (1992): A simplified approach to assessing adult chronic energy deficiency. Eur. J. Clin. Nutr. 46,173-186.

Hop LT, Hoa PT, Hau CT & Khoi HH (1991): Nutritional status of pregnant and breastfeeding women at central Hanoi city and some northern rural areas. J. Hygiene Epidemiol. 48,3.

James WPT, Ferro-Luzzi A & Waterlow J (1988): Definition of chronic energy deficiency in adults. Report of a working party of the International Dietary Energy Consultative Group. Eur J. Clin. Nutr 42,961-981.

Khoi HH (1990): Protein energy nutritional status of rural people in some regions of Vietnam. Praca Izz No. 53, Warsaw.

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Strickland: What altitude are your people living at in mountainous regions? Do you think the effects you found are related to socio-economic conditions or to altitude hypoxia?

Ha Huy Khoi: These data are not very representative, but they live in the lower parts of the mountains. The energy intake and fat intake are higher than in urban areas. We need data on people living in high mountainous areas.

Allen: If you accept the 18.5 cut-off, then 50% of women in the 41-50 year age group and more over 60 are in this category. Do you accept that all these people in your country are short of food?

Ha Huy Khoi: It is a problem of energy intake because they work so hard.

James: Are you confident enough of your data to tell your government to put more money into the areas where there are most women with low BMI?

Ha Huy Khoi: Yes.

Thompson: Can the BMI of the mother be a proxy for the status of children under five? Would the BMI of pregnant women predict low birth weight: looking at weight gain in pregnancy is difficult because of the need for regular weighing.

Ha Huy Khoi: Yes to your first question, but many variables affect birth weight and we do not have data on this.

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